After more than 30 years in space heading away from Earth, Pioneer 10 has sent its last signal home.

Pioneer 10 heads for deep space

The distant emissary, over 12 billion kilometres away, will now disappear into the galaxy.

Pioneer's last, very weak signal was received on 22 January, after which US space agency (Nasa) engineers reported that its power source had decayed such that it might not be capable of sending another message.

Because of this, Nasa has said it has no further plans to contact Pioneer 10.

The spacecraft will be left to drift among the stars carrying a message on its side from the creatures that made it.

Scientifically rich mission

"Pioneer 10 was a pioneer in the true sense of the word," says Colleen Hartman, director of Nasa's Solar System Exploration Division. "After it passed Mars on its long journey into deep space, it was venturing into places where nothing built by humanity had ever gone before.

"It ranks among the most historic as well as the most scientifically rich exploration missions ever undertaken."

Nasa's Larry Lasher adds: "Originally designed for a 21-month mission, Pioneer 10 exceeded all expectations and lasted more than 30 years."

Pioneer 10 was launched on 2 March, 1972, on a three-stage Atlas-Centaur rocket, reaching the speed of 52,150 km per hour needed for the flight to Jupiter.

It was the fastest object to leave the Earth, being fast enough to pass the Moon in 11 hours and to cross Mars' orbit, about 80 million km away, in just 12 weeks.

In July, 1972, Pioneer 10 entered the asteroid belt becoming the first spacecraft to pass through it.

Destination Aldebaran

It reached Jupiter on 3 December, 1973, becoming the first craft to obtain close-up images of the gas giant and to chart its intense radiation belts.

Flying past Jupiter, it became the first human-made object to pass the orbit of Pluto, the most distant planet from the Sun.

Following its encounter with Jupiter, Pioneer 10 explored the outer regions of the Solar System, studying the solar wind as well as cosmic rays from deep space.

Since its official science mission ended on 31 March, 1997, Pioneer's weak signal has been tracked by Nasa's Deep Space Network as part of a new study of communication technology in support of a future Interstellar Probe mission.

At last contact, Pioneer 10 was 12.2 billion km from Earth, or 82 times the normal distance between the Sun and the Earth.

At that distance, it takes more than 11 hours and 20 minutes for the radio signal, travelling at the speed of light, to reach the Earth.

Almost forever

"We send our thanks to the many people at the Deep Space Network and the Jet Propulsion Laboratory (JPL), who made it possible to hear the spacecraft signal for this long," says Pioneer 10 Flight Director David Lozier.

Mankind's first emissary into space carries on its side a gold plaque that describes the creatures that built it, where we are and the date when the mission began.

Like a ghost ship, Pioneer 10 will continue to coast silently through space, heading for the red star Aldebaran.

It will take Pioneer 10 more than 2 million years to reach it. Its sister ship, Pioneer 11, ended its mission in September 1995, when the last transmission from the spacecraft was received.

Both Pioneer spacecraft and Voyagers 1 and 2 could outlast the Earth.

Long after our Sun has swollen into a red giant and destroyed our planet, these four spacecraft will still be drifting silently amongst the stars, almost forever.